This invention relates generally to the manufacture of carboxylic anhydrides, and more particularly to novel catalysts and methods for their use in manufacturing carboxylic anhydrides by molecular oxidation of hydrocarbon feedstocks, in particular the manufacture of phthalic anhydride by molecular oxidation of orthoxylene.
Aromatic carboxylic anhydrides are widely produced in large quantities through the molecular partial oxidation of hydrocarbon feedstocks, particularly phthalic anhydride from orthoxylene. The phthalic anhydride product is commercially useful for reactions with alcohols, such as oxo-alcohols to form the corresponding phthalic anhydride alcohol esters, which find use as plasticizers and lubricants.
Catalysts for the above partial oxidation, in which vanadium pentoxide is deposited on titania, are known in the art. The art has sought to develop improved and promoted catalysts in order to enhance the activity and selectivity for the phthalic anhydride fraction.
U.S. Pat. Nos. 3,464,930, 3,509,179, 3,684,741 and 3,909,457, and British Pat. Nos. 1,140,264 and 1,237,954, to BASF disclose catalysts prepared by depositing vanadium pentoxide-titanium dioxide on a carrier which is optionally primed with an oxide of the metals vanadium, molybdenum, tungsten, cobalt, zirconium, chromium, titanium, iron or mixtures thereof.
See also S. Matsuda et al., Applied Catalysis, 8 (1983) 149-165, for discussion of titanium dioxide catalysts in general, including mixed oxides composed of TiO.sub.2 and MoO.sub.3.
U.S. Pat. Nos. 4,052,418 (1977) and 4,234,461 (1980) to Standard Oil Company illustrate a promoted catalyst in which the vanadium pentoxide is admixed with an oxide of at least one of the group of boron, niobium, tantalum, antimony, tungsten and chromium (with or without one or more of the group of alkaline metals, zinc, cadmium, phosphorus, arsenic, copper, cerium, thorium, tin, manganese, iron and uranium). The catalysts are prepared by digesting the vanadium pentoxide and the selected promoter oxide in hydrochloric acid followed by drying at 120.degree. C. See also U.S. Pat. Nos. 4,075,231 and 4,076,731 to Standard Oil Company which disclose oxide catalysts containing molybdenum or tungsten among other metals. U.S. Pat. No. 4,293,449 (1981) to Standard Oil Company describes a high surface area catalyst consisting of a support material such as silica, alumina, alumina-silica, silicon carbide, titania and zirconia and a high-surface area coating to which is applied solutions of ammonium heptamolybdate, ammonium hydroxide or cobalt nitrate.
U. K. Published Application No. 640,555 describes an oxidation catalyst comprising a ground layer and surface layer wherein in both layers ferric oxide may be replaced in whole or in part by other oxides such as chromium or manganese sesquioxide, vanadium sesquioxide, cobalt oxide, thorium oxide or other of the transition metals.
U.S. Pat. No. 3,721,683 (1973) to Teijin Chemicals Limited discloses catalysts obtained by calcining a mixture of a vanadium compound, a chromium compound, and a promoter metal component, the vanadium and chromium being present in an atomic ratio of 1:0.5 to 1:1.
Vanadium pentoxide monolayer catalysts have been studied and discussed in A. J. Van Hengstum et al., Applied Catalysis, Vol. 8, 369-382 (1983); M. Gasior et al., Applied Catalysis, vol. 10, 87-100 (1984); G. C. Bond et al., Faraday Discussions of the Chemical Society, vol. 72, 235-246 (1981), and G. C. Bond et al., Journal of Catalysis, vol. 77, 309-322 (1982).
Commonly-assigned U.S. Pat. No. 4,582,911 discloses phthalic anhydride catalysts prepared by the steps of forming a catalyst precursor by depositing on titanium dioxides solids in the anatase form a discontinuous monolayer amount of at least one source of tantalum oxide, calcining the thus-formed catalyst precursor under conditions sufficient to convert the tantalum oxide source into the oxide form, depositing upon the calcined catalyst precursor a catalytically effective amount of at least one vanadium compound which is convertible into vanadium oxide upon heating and calcining the vanadium-deposited solids under conditions sufficient to convert the vanadium compound into vanadium oxide.
Commonly-assigned U.S. Pat. No. 4,582,912 discloses a phthalic anhydride catalyst prepared from sources of vanadium oxide, titanium oxide and the oxide of a promoter metal selected from Sb, Ga, Ge, In, Tl, Pb, Se, Te, P and Bi. The catalyst is prepared by a process of sequential deposition wherein at least a continuous monolayer amount of a vanadium oxide source is first deposited on TiO.sub.2 anatase to form a catalyst precursor which is then calcined; and thereafter a vanadium oxide source and the oxide of at least one of the aforementioned reactive metals are deposited on the calcined catalyst precursor, the resulting catalyst solids then being calcined.
Commonly-assigned U.S. Pat. No. 4,728,744, which is also hereby incorporated by reference, discloses a sequential deposition process for forming a zirconia based catalyst wherein a source of zirconium oxide is deposited in an amount sufficient to provide a continuous monolayer on titanium dioxide solids in the anatase form; the thus-formed catalyst precursor is then calcined; and a source of vanadium oxide is then deposited on the calcined catalyst precursor; and the catalyst is again calcined.
The catalysts in the foregoing commonly-assigned patents may also comprise effective amounts of promotor metal oxides selected from the group consisting of niobium, magnesium, calcium, scandium, yttrium, lanthanium, uranium, cerium, chromium, magnanese, iron, cobalt, nickel, copper, zinc, aluminum, gallium, indium, silicon, germanium, tin, bismuth, antimony, tellurium, lead, hafnium, alkali metals (Cs, Rb, K, Na, Li) and mixtures thereof.